Heat pump water heaters, such as the one described in Japanese Laid-open Patent Publication No. 60-164157, are known which are capable of utilizing a heat pump cycle to heat water. Such a heat pump water heater has primarily a compressor, a refrigerant/water heat exchanger, and a heat-source-side heat exchanger, and is configured so that water is heated by the radiation of refrigerant in the refrigerant/water heat exchanger, and the hot water thereby obtained is fed to a storage tank.